Sustainer voltage generator

ABSTRACT

There is disclosed an improved sustaining voltage supply system, particularly for driving a capacitive load, as for example a gas discharge display panel having row-column conductor arrays, the matrix cross points of which are non-conductively coupled to a gaseous discharge medium in the panel. In a preferred arrangement, a pair of series connected, constant current transistor circuits, clamped by parallel diodes, have the intermediate points thereof connected to supply the sustainer voltages to the panel. There constant current sources are connected across the direct current voltage source so that the displacement currents to the panel are supplied with very low notching on high current commands with better tracking of input signals thereto.

United States Patent [191 Leuck June 28, 1974 [54] SUSTAINER VOLTAGE GENERATOR l rinuiry tdrniner l lermankarl S aalhach 2 d D. be k T 1 d ,0hi Assistant Examiner-Lawrence J. Dahl [75] Inventor Donal 0 e O Attorney, Agent, or Firm-E. J. Holler; Donald Keith [73] Assignee: Owens-Illinois, lnc., Toledo, Ohio Wedding 22 F'led: Oct. 19 1971 1 1 57 SCT [21] Appl 190614 There is disclosed an improved sustaining voltage supply system, particularly for driving a capacitive load, as for example a gas discharge display panel having [52] US. Cl 315/169 TV, 315/169 R, 328/ 1 ow-column conductor arrays, the matrix cross points [51] Int. Cl. H05b 37/00 f hi h are non-conduotively coupled to a gaseous Fleld of earch 307/264; 315/169 TV, 169 R; discharge medium in the panel. In a preferred arrange- 330/11, 207 P; 328/183 ment, a pair of series connected, constant current transistor circuits, clamped by parallel diodes, have the intermediate points thereof connected to supply the sustainer voltages to the panel. There constant [56] Reterences cued current sources are connected across the direct cur- UNITED STATES PATENTS rent voltage source so that the displacement currents 3,513,327 5/1970 Johnson 315/169 R X to the panel are supplied with very low notching on 3,526,846 9/1970 Campbell 330/11 high urrent commands with better tracking of input signals thereto.

6 (Ilaims, 8 Drawing Figures I COMMON SELECTION MATRIX SELECTION MATRIX PMENTEDJUN281974 3321.596

SHEET 1 (IF 2 /3-/ l6 1 /7 a0 In/5 '3 Row /2 CONDUCTOR. GAS

SELECTION DISCHARGE MATRIX PANEL /0 COLUMN Z1 CONDUCTOR. SELECTION MATRIX ,32

SUSTAINEFL CONTROL 3/ CIRCUIT FIG. 1

l ccz/dok I SELECTION MATRIX SELECTION MATRIX VTQ'BK v I COMMON FIG. 4

PMENIEDJUW? IBII 3.821; 596

SHEET 2 0F 2 4/ l =swITcI-I a CLAMP I I LEVEL VOLTAGE 4:1 VCC VT 41 542 ARE 43 TO PANEL & sELEcTIoN MATRIX coNsTANT CURRENT DEVICES C I P 44- a 45 ARE I SWITCH & CLAMP DIODES IQ 2 T 42 COMMON FIG. 2

VP 0 TYPICAL susTAIN VOLTAGE I I TYPICAL I (FIGZ) WITHOUT 0 I FIRING T PANEL FIG. 33

I I l TYPICAL 1 (FIG.2) WITHOUT 2 O FIFUNG T PANEL A DISPLACEMENT CURRENT ID To PANEL AT PULL-UP NET LOOP cuIuLENT THROUGH v SUPPLY oN PuLL-uP SIDE I D RJNG PULL-UP SUSTAINER VOLTAGE GENERATOR The present invention is directed to a sustaining voltage supply system which is particularly and uniquely designed for driving gaseous discharge display panels of the type disclosed in Baker et al. US. Pat. No. 3,499,167. Sustaining voltage generators constituting such systems supply operating power to gaseous discharge devices wherein the cross conductor arrays e. g. the row and column conductors, are dielectrically isolated from the discharge medium so as to not be in conductive contact therewith and the load on the generator is essentially capacitive in nature. Thus, some aspects of instant design are dictated by power and voltage frequency requirements of the panel, the frequency being in the range of about 50 kHz. Because of the nonlinearity of the impedance presented by the panel to the generator, and the pulsing nature of the discharges in the panel so that the load currents are pulsing in nature, distortion in the sustaining voltage waveform can adversly effect the operating characteristics. Accordingly, the present invention is directed to a sustaining vvoltage generator for gas discharge display panels having lower notching in the waveform of the sustainer voltage as applied to the panel on current demand and better tracking input control pulses. Moreover, the device, in accordance with the present invention, has the advantage of shifting the load switching burden from relatively slow power transistors to passive diode devices. According to the invention, a pair of switchable constant current devices are connected in series across a supply voltage source with the intermediate point between the two constant current devices being connected to the conductor arrays of the panel. A switch and clamp diode is connected in parallel with each constant current device and has a bias voltage associated therewith which is equal to a selected switch and clamp level voltage. As used herein, notching or notch distortion means the distortion in the sustainer voltage wave form caused by the firing of a large number of discreet sites in the display panel served by a common sustaining generator.

BRIEF DESCRIPTION OF THE DRAWINGS The above and other objects, advantages and features of the invention will become more apparent in light of the following specification taken in conjunction with the accompanying drawings wherein:

FIG. 1 is a diagrammatic illustration of the gaseous discharge display panel to which the invention has been applied,

FIG. 2 is a simplified circuit diagram illustrating the principles of the invention,

FIGS. 3A, 3B, 3C, 3D and 3E are waveform diagrams of typical sustaining voltage and current waveforms and FIG. .4 is a complete circuit diagram illustrating the invention in its preferred form.

Referring to FIG. 1, the gaseous discharge display panel is generally of the type disclosed in Baker et al US. Pat. No. 3,499,167 and is constituted by a pair of support plates 11 and 12 on which are placed row conductor array 13 and column conductor array 14, the conductor arrays having dielectric or insulating coatings l5 and 16 applied thereto so that there is no conductive current passing from the conductors via the dielectric coating to the gaseous medium, that is, the

matrix cross points defined by the cross conductor arrays are non-conductively coupled to the gaseous discharge medium in the panel. The: respective plates are joined in spaced apart relation by a spacer sealant means 17 to form a thin gaseous discharge chamber into which may be placed a neonargon gas mixture as is disclosed in Nolan application Ser. No. 764,577 filed Oct. 2, 1968. Other gaseous discharge mediums may likewise be incorporated in the panel but the improvement achieved by the use of the gas mixture recited above permits the panels to be operated in the 30-50 kHz range without being damaged by thermal shock and at the same time with good light output and good memory margins. The individual conductors in row conductor array 13' are preferably driven by row contively. The selection matrices 20 and 21 receive input signals from a signal source, not shown, but which may be a computer, keyset, tape reader or other data source.

A pair of sustaining generator voltage sources 30 and 31 are provided for supplying opposite phase or opposite polarity sustaining potentials to the row conductor I array 13 and the column conductor array 14 in the panel 10, the voltages having the waveforms shown in FIG. 4 on the line leading to the gas discharge panel 10.

Essentially, one-half of the sustainer potential as applied to the panel is applied to row conductors and the other onehalf of the sustainer potential is applied to the column conductors it being noted that the sustaining generators 30 and 31 have a common point or terminal (which is not necessarily electrical ground) so that in the arrangement shown, the discharge condition manipulating potentials generated in or produced by row conductor selection matrix 20 floats or is referenced to the potential from the sustainer generator source 30 and similarly the discharge condition manipulating potentials generated in the column conductor selection matrix are in series with and have as a reference point the instantaneous voltage from sustaining generator 31. Moreover, both sustaining generators 30 and 31 receive controlling or logic input signals from a source 32 which if desired, may be a free running multivibrator or other controllable signal source from the computer. Thus, it may be desirable at times to erase the pane in which case one of the signals applied to one of the sustainer generators 30 and 31 may simply be removed for a certain time interval to thereby permit bulk erasing of all information on the panel or it may be desirable to vary the sustaining rate by varying the sustaining rate from control circuit 32.

Referring now to FIG. 2, a sustaining voltage generator in accordance with the present invention is essentially constituted by a pair of constant current devices 41 and 42 which have an intermediate point 43 therebetween which is connected via one of the matricing circuits shown in FIG. 1 to the respective row or column conductors on the panel. A capacitance Cp is diagrammatically illustrated as being connected to the in termediate point 43 as the equivalent panel capacitance. It will be appreciated that this capacitance is the panel capacitance per se and is not necesarily present as a separate component.

Paralleling each constant current source 41 and 42 are switch and clamp diodes 44 and 45, respectively, each of which has its own, properly poled, bias voltage which is equal to the switch and clamp level voltage V It will be noted that diode 44 has its anode connected to the intermediate point 43 and its cathode connected to the negative terminal of the switch and clamp voltage V with the positive terminal of the bias supply V is connected to the operating voltage Vcc. As indicated, the operating voltage Vcc is very much greater than the switch and clamp voltage V With respect to the sustainer voltage waveform as shown in FIG. 4, it will be noted that the waveform of the voltage appearing betwen the row and column conductors at any discrete selected sites, rises or is pulled up from about to about the Vcc level, stays at the Vcc voltage level for a selected time interval, is then returned or pulled down to the O or reference voltage level where it stays for a selected time interval and is then driven to a negative (as seen by the gas in the panel at the sites) Vcc volt level, stays there for the same time interval as at the positive level and, then is returned to the O or reference voltage level where it remains for a selected time interval and then repeats itself. Such a voltage waveform is in effect, the differences between the two voltage waveforms applied to the x(row 13) and y(column l4) conductors shown in the drawings. The time intervals shown are exemplary. However, the timing of the pull up and pull down intervals is set by the computer or other source and may be adjusted as desired. For example, the pulled up interval may be made longer or shorter than the pulled down interval and it may be desirable in some cases to make the voltages applied to the respective row and column conductors have different time intervals (as for example to remove one half the sustainer voltage for erase of one entire panel). At any rate, the time intervals are easily adjusted by the timing of the occurrences of the control pulses for switching the alternate on and off states of the constant current devices to be described later herein.

Indicated at the point x on the pulled up pulse, the firing of a large number of discreet sites along a number of selected conductors, and as driven by one sustaining voltage source causes a relatively heavy current and can cause notch distortion. In accordance with a major feature of this invention, the current levels is set to be constant by the use of constant current devices 41 and 42 and hence, the notch distortion due to heavy current flow is avoided. Moreover, the load switching burden e.g. I current switching, is shifted from the relatively slow power transistors to the passive diode devices. The idealized waveform diagrams of FIG. 3 illustrate the operation. It will be noted that the current waveforms of FIG. 3D and FIG. 3E show the displacement and loop currents which charge the panel capacitance.

Referring now to FIG. 4, the invention is shown as applied with typical operating parameters. In this case, the Vcc voltage level is at about 140 volts, and the V voltage level is about 8 volts. It will be appreciated that the sustain generator for the opposite panel conductor arrays would be the same as shownin FIG. 4. It willbe noted that the collector-emitter circuits of transistor O1 in constant current device 41 and the collectoremitter circuit of transistor Q2 are series connected and that the collector resistors R1 and R2 are of very low value (about 4 ohms). The collector-base circuit of transistor 01 is connected in circuit with the collectoremitter circuit of transistor 03 and a similar connection is made in connection with the collector-emitter circuit of transistor Q4 and transistor Q2. A small resistor R3 (about 10 ohms) is connected between the base of transistor Q1 and the emitter thereof and a similar resistor R4 is connected between the base of transistor Q2 and the emitter of transistor Q2. The base of transistor Q3 receives a turn on current through R6 when O5 is switched on, and a turn off bias through R5 when Q5 is switched off. Transistor Q5 has its emitter connected to a point of common potential or ground and the base thereof receives a low voltage logic operating or control pulse from the computer 32 or other source shown in FIG. l.

The resistor R6 shown in FIG. 4 is used as the base drive resistor and is controlled by operating transistor Q5. Transistor Q6, it will be noted, has a resistor R7 connected to a source of potential of about 8 volts with the emitter of transistor Q6 being connected to the common bus for or ground source for the Vcc supply. A similar control or logic pulse voltage is applied to the base of transistor Q6 and having the timing characteristics described earlier. Transistors Q5 and Q6 control the conductive conditions of constant current devices 41 and 42 respectively. These constant current devices are turned on and off in the manner described above so as to pull up and pull down" the potential at intermediate-point 43 and hence the sustainer voltage for one of row or column conductors shown for the panel. It will be noted that these are displaced slightly in time so as to produce the voltage waveform shown as being applied to the gas in the panel as opposed to the voltage waveform which is applied to the column and row conductors. Thus, the times of occurrences of the charging of a panel and the discharging of same, both on the negative and positive excursions of the row and column voltage sustainer waveforms is controlled by the input from the control circuit 32. It will be appreciated that there may be a number of circuits similar to that described for supplying groups or sectors of the panel with sustainer voltages from separate sources.

It will be apparent that many other embodiments, modifications and changes are possible and it is intended to encompass such obvious modifications and changes in the scope of the claims appended hereto.

What is claimed is:

1. A sustainer voltage supply system for a capacitive load, gas discharge display panel having row-column conductor arrays, the matrix cross-points of which are non-conductively coupled to a gas discharge medium in the panel said sustainer voltage supply system comprising a pair of sustainer voltage generator means, one for the row conductor array and one for the column conductor array, the improvement wherein each said sustainer generator means is constituted by,

a pair of series connected, separately switchable alternately on-off constant current sources, means connecting an intermediate point between said constant current sources to the conductors in an array,

diode means, one said diode means for each said constant current source and connected in shunt wit its respective on-off current source, and

controll means connected to said constant current sources for controlling said alternate on-off switching operation thereof.

2. The invention defined in claim 1, each said constant current device including a pair of compound connected transistors.

3. The invention in claim 1 including a voltage means connected to said diode means for establishing a switch and clamp level voltage therefor.

4. The invention in claim 3 wherein the voltage of said voltage means is very much less than the voltage level of sustainer voltage applied to said conductor arrays.

5. A square wave voltage power supply for a relatively high power capacitive load, said square wave voltage being substantially free of distortion due to supplying heavy currents to said capacitive load, comprising a pair of square wave sources each of said pair of sources including;

a pair of switchable constant current devices, means connecting said constant current devices in series circuit across said source of direct current voltage, clamp diode means, one for each constant current device and connected in shunt therewith and means for controlling said constant current devices,

such that they are alternately on and off and to apply said high voltage from said source to said intermediate point and said load and supply a displacement current thereto and therefore, respectively.

6. A power supply for a high power capacitive load comprising a direct current voltage source,

a pair of switchable constant current devices connected in series across said voltage source with an intermediate point therebetween connected to said capacitive load,

a clamp diode circuit connected to shunt with each said constant current devices, respectively, and

control circuit means connected to each said constant current devices for alternative controlling the on and off conditions of said constant current de- 

1. A sustainer voltage supply system for a capacitive load, gas discharge display panel having row-column conductor arrays, the matrix cross-points of which are non-conductively coupled to a gas discharge medium in the panel said sustainer voltage supply system comprising a pair of sustainer voltage generator means, one for the row conductor array and one for the column conductor array, the improvement wherein each said sustainer generator means is constituted by, a pair of series connected, separately switchable alternately on-off constant current sources, means connecting an intermediate point between said constant current sources to the conductors in an array, diode means, one said diode means for each said constant current source and connected in shunt with its respective on-off current source, and controll means connected to said constant current sources for controlling said alternate on-off switching operation thereof.
 2. The invention defined in claim 1, each said constant current device including a pair of compound connected transistors.
 3. The invention in claim 1 including a voltage means connected to said diode means for establishing a switch and clamp level voltage therefor.
 4. The invention in claim 3 wherein the voltage of said voltage means is very much less than the voltage level of sustainer voltage applied to said conductor arrays.
 5. A square wave voltage power supply for a relatively high power capacitive load, said square wave voltage being substantially free of distortion due to supplying heavy currents to said capacitive load, comprising a pair of square wave sources each of said pair of sources including; a pair of switchable constant current devices, means connecting said constant current devices in series circuit across said source of direct current voltage, clamp diode means, one for each constant current device and connected in shunt therewith and means for controlling said constant current devices, such that they are alternately on and off and to apply said high voltage from said source to said intermediate point and said load and supply a displacement current thereto and therefore, respectively.
 6. A power supply for a high power capacitive load comprising a direct current voltage source, a pair of switchable constant current devices connected in series across said voltage source with an intermediate point therebetween connected to said capacitive load, a clamp diode circuit connected to shunt with each said constant current devices, respectively, and control circuit means connected to each said constant current devices for alternative controlling the on and off conditions of said constant current devices. 